The present invention relates to unsaturated polyester resin compositions. In one of its aspects it relates to processes for making unsaturated polyester resin compositions. In still another aspect this invention relates to controlling the volatilization of the styrene ingredients utilized in unsaturated polyester resin compositions.
Unsaturated polyester resins are a class of soluble, essentially linear, low molecular weight, macromolecules which contain both carboxylic ester groups and carbon carbon double bonds as recurring units along the main chain. Unsaturated polyesters can be prepared by the condensation of (a) ethylenically unsaturated dicarboxylic acids or their anhydrides to impart unsaturation, (b) saturated dicarboxylic acids or their anhydrides to modify the unsaturated polyesters and (c) dihydric alcohols.
Unsaturated polyester resin compositions can include monomeric styrene as a copolymerizable monomer. A solution of monomeric styrene and unsaturated polyester resin is frequently identified as polyester resin syrup. Styrene customarily is present in an amount ranging from about 20 to about 50 weight percent of the syrup. When polyester resin syrup is employed in hand layup or spray applications to produce glass fiber reinforced plastic products and the like, styrene monomer in the syrup has a the tendency to volatilize. Volatilization of the styrene is objectable for several reasons: among others (1) the cost of the lost styrene is appreciable, (2) the variable loss of styrene from day to day and batch to batch can result in non-uniform product performance, and the presence of styrene vapors in the atmosphere at the work place constitutes both a health hazard to workers and a fire hazard.
There exists a need, therefore, to provide compositions of polymerizable unsaturated polyester resin including monomeric styrene in which the volatilization of styrene is successfully suppressed to acceptable levels without adversely affecting the characteristics of the resulting products.
An object of this invention is to provide an unsaturated polyester resin that reduces the volatilization of styrene. Another object of this invention is to reduce the overall resin costs or to improve physical and mechanical properties of the polyester, preferably both.